In Augustine's Commentary to the Galatians, there is a particularly complicated sentence. I can understand the parts of it and generally make sense of it, but I'm struggling with the sentence structure. What is the main clause, and how do the subordinate parts fit together?

Wow, what a mouthful. I like to read things following the Latin order as much as possible, so here is how I took it - exactly as you did I think... the ostendit does indeed seem to introduce two different indirect statements, but they are nicely coordinated with et...et... - ostendit BOTH (that his critics are not divinely sanctioned) AND (that he should not be considered inferior to the other apostles).

Quamquam et ipsa salutatione - Yet even in the salutation itself,

cum dicit - when he says that se Apostolum - he (is) an Apostlenon ab hominibus - not from menneque per hominem - nor through a man

quod - something whichin nulla alia epistola - in no other letterdixisse invenitur, - he is found to have said

satis ostendit - he clearly shows

et illos - BOTH that those menqui talia persuadebant - who urge such things (i.e. Jewish law)non esse a Deo - are not from God,sed ab hominibus - but from men

et ceteris Apostolis - AND that (compared) to the other Apostles,quantum - so farad auctoritatem testimonii evangelici pertinet - as it pertains to the authority of his evangelical testimony,imparem se haberi non oportere - he should not be considered unequal;

quandoquidem non ab hominibus - since indeed not from menneque per hominem - not by a man,sed per Iesum Christum - but by Jesus Christet Deum Patrem - and God the Fatherse Apostolum noverit - he knew that he was an Apostle.

Thanks. I missed the "et...et" for a long time, so I was trying to read "sed ab hominibus et ceteris Apostolis" as a phrase. I've noticed that Augustine likes lots of indirect statements in long sentences. I suppose, though, that's representative of Latin in general.

Plus, reading Paul is bound to be a bad influence, ha ha... there are some passages in Paul that are a grammatical labyrinth. Admittedly, Augustine was reading Paul in Latin rather than Greek, and I've never studied Paul carefully in Latin ... but in Greek, he can really leave you scratching your head sometimes!